Box-shaped ducts are extensively used in heating and ventilating systems to distribute heated or cooled air throughout a structure. The ducts are commonly formed in sections of predetermined length which are then connected to form a continuous air distribution duct. The material from which the duct sections are formed is sheet metal of the desired gauge fed from a roll or coil of material. As the sheet metal uncoils, it is flattened or straightened to remove the curved set in the material that exists from it being coiled. The sheet metal is then notched along its side edges at predetermined distances where the corners of the duct section will be formed. A shear then cuts the material into blanks of a length necessary to form a finished duct section. This notched blank is then moved 90 degrees onto a roll former to form the male and female portions of the Pittsburgh seam at the opposite ends of the blank. The blank is then transferred once again, usually 90 degrees, into a roll former to form the flanges that will provide for connection of the individual duct sections. When the flanges have been formed, the blank is then transferred to a sheet metal break where three 90 degree bends are made to form the box-shaped section. Obviously, this process involves the repeated handling of individual pieces and the transfer of them from one machine to another throughout the forming process. It is not only time consuming to transfer these blanks from machine to machine, but it requires a considerable amount of floor space for the equipment, conveyors and transfer tables between the pieces of equipment. Moreover, roll forming of the male and female portions that form the Pittsburgh seam frequently distorts the sheet metal with the result that the seams are not straight making it more difficult to complete the duct section and lock the seam on the job site when the sections are and assembled into a continuous air distribution duct.
There is therefore a need for an improved method and apparatus for forming box-shaped duct sections with male and female Pittsburgh seams.
To fulfill the foregoing need, it is an object of the invention to provide an improved method and apparatus which will minimize the amount of floor space required to carry out the complete forming process.
It is a further object of the invention to provide an improved method and apparatus that will provide for forming the box-shaped duct sections more quickly and efficiently and at a lower cost.
The improved method and apparatus of the invention fulfills all of the foregoing needs and objects while producing a product that is of an improved quality.